Conventionally, a fan is installed to a control device of a machine tool and the like so as to cool the control device. The fan is exposed in a wet environment subjected to water, cutting fluid and the like, since the fan is located in the vicinity of the machine tool and the like. Therefore, the fans provided with an oil resistant and water resistant structure (hereinafter, merely referred to as “a waterproof structure”) are known in use for the control device of the machine tools and the industrial machines, as described in Japanese Patent Application Laid-Open Publications No. 2003-230246 and No. 2011-78224.
FIG. 7 shows a cross-sectional view of a fan provided with a waterproof structure disclosed in Japanese Patent Application Laid-Open Publication No. 2003-230246. The fan shown in FIG. 7 has a structure in which a mold portion is formed by an insulating resin 106 as follows. A stator assembly 103 with a circuit board 102 and a stator 101 is mounted to a bearing housing (bearing supporting cylindrical portion) 105a of a casing 104, and then a forming mold 108 is fixed to the casing 104. An insulating resin 106 is injected into the mold 108, so that a space portion 107 between the bearing housing 105 and a plate-like portion 105b of the casing 104 includes the stator 101 and the circuit board 102 therein, and the molded portion is formed by the insulation resin 106.
FIG. 8 shows a technology for forming a molded portion of the fan equipped with a waterproof structure disclosed in Japanese Patent Application Laid-Open Publication No. 2011-78224. According to the technology for forming a molded portion of the fan shown in FIG. 8, an epoxy resin 204 is poured into a mold 203 after placing a stator 200, a circuit board (PC board) 201 and a lead wire 202 between an upper die 203a and a lower mold 203b of the mold 203, and the resin molded portion is formed in one piece.
As described above, according to the technology described in Japanese Patent Application Laid-Open Publication No. 2003-230246 and the technology described in Japanese Patent Application Laid-Open Publication No. 2011-78224, the resin molded portion is formed using a forming mold in order to make the stator and the circuit board to be a waterproof structure.
However, in the method of forming a resin molded portion using a forming mold, there was a need to set an intermediate assembly composed of a stator attached with a circuit board to a forming mold individually, and so there existed a problem that several working steps were required. In addition, the insulating resin injected into the forming mold required certain period of time for curing. For this reason, in performing an efficient mass production, it was necessary to prepare not only one but a plurality of forming molds and use them simultaneously in order to proceed other operations in parallel while waiting the curing of the insulating resin. Therefore, there existed a problem that the cost was high.